AnimalsMind-BlowingEvery winter there's a migration bigger than the Serengeti's - and almost nobody has heard of it. Hundreds of millions of sardines surge up South Africa's east coast in a shoal over 7km long. Dolphins herd them into bait balls near the surface. Sharks rush in from below. Cape gannets plunge at up to 86km/h and a Bryde's whale swallows the whole ball in one pass. Scientists still debate why the sardines bother.2 hours ago